Same problem here. I have spent several hours over the last few weeks striving to find what is causing the problem. Perhaps a guilty process or service that might be discovered with Task Manager, Process Explorer or Process Monitor. Reading this post I realize the problem is with Update 1809, not something that I installed or tweaked.
It is important for me because I create new folders and/or files several times a day. A 15 second delay is too much and it is obviously a problem that must be solved.
What is ironic is that this site's address is "answers.microsoft.com". I see a lot of questions but no answers, just replies from a lot of users having the same difficulty. Is anybody from Microsoft listening?